1. Field of the Invention
The invention relates to gelled polymers and measurement of adhesion of such polymers to surfaces including plastic surfaces of connectors for cables and wires that form telecommunications and power distribution networks. More particularly this invention relates to photocurable organopolysiloxane sealing gel compositions and an apparatus for measuring the strength of the adhesive bond of cured sealing gels to plastic.
2. Description of the Related Art
Many of the technologies available to modern society find their origin in the application of electricity and electronics. The driving force of electricity coupled with the versatility of electronics has produced, for example, the communications, automation and computer industries. There are many specialized fields associated with each of these industries. Communications may be divided into space and satellite communications, commercial radio and television, data communications, navigation systems, radar and police and aircraft communications, to name but a few. A common feature of these communication systems is the development of networks linking together a multitude of transmitting and receiving sites. Network links may be hard wired or in the form of radio signals, with most communications systems requiring both types. Much of the infrastructure of communication networks exists in open environments at the mercy of inclement weather and climatic events including rain, hail, and snow storms. Electricity distribution networks and telephone communications networks are particularly vulnerable to erratic changes in climate. Some network components, such as cables and wire connectors may be particularly susceptible to attack that interferes with network and signal integrity in adverse weather conditions. Attack of network connectors by contaminants takes a variety of forms of which ingress of liquids or moisture is one of the most common. The presence of seams or gaps in a connector will provide access to moisture and other liquid contaminants that could compromise network integrity by causing a short circuit. For this reason, it has become common to use sealed connectors at relatively unsheltered network connecting sites, such as those used by telephone companies to provide service from the telephone line twisted pair to an individual household. The network to home connection typically resides inside an enclosure or pedestal box mounted at ground level, and exposed to the elements.
Evidence of the benefits of sealed connectors in telecommunications networks is given in U.S. Pat. No. 5,975,945 describing a network interface device (NID) between a cable and a local network including a number of telephones. A conventional 5-pin plug-in protector provides electrical isolation when inserted in the NID to form electrical connections. Water resistant gel, applied to each plug-in protector, forms a water-resistant seal to inhibit moisture penetration into the protector, thereby allowing it to be used outdoors, even though, under conventional NID specifications, plug-in protectors are limited to indoor applications and special potted protectors are required for outdoor use.
U.S. Pat. No. 5,079,300 addresses the use of gel sealants that also prevent corrosion of e.g. connectors used in telecommunications networks. Suitable gel materials include silicone compositions that environmentally seal and protect substrates such as electrical connections, bare electrical conductors and electrical splices.
Requirements for gel sealants include the need to protect and insulate electrical connections and splices at temperatures that could vary from about −40° C. to about 60° C. or more. Gel sealants should provide moisture and watertight containment for wire junctions as well as preventing rodent and insect damage. The need to reenter a pedestal box to alter or repair wires, and connections between wires, requires that cured gels withstand considerable and repeated deformation during making and breaking of connections, for example, to modify service to a consumer or to re-route a telephone signal. It should be possible to insert and withdraw connecting wires without significant transfer of gel sealant to the bare wire or loss of sealant from the socket from which the wire is withdrawn. It is desirable that gel sealants, meeting these requirements, possess high elasticity and elongation related to high deformability. Suitable materials have higher cohesive strength than adhesive strength yet maintain sufficient adhesion to connector surfaces that the gel remains substantially within the connector during retermination. Hydrolytic stability and stability against thermal and oxidative degradation lower the probability of gel mass shrinkage, which could open up channels for ingress of moisture and fluid contaminants.
Known gel materials, for use in wire and cable connectors, include those derived from polyurethane and silicone polymers as revealed in U.S. Pat. No. 5,934,934 describing a gel filled connector for connecting electrical wires. The connector includes a housing to receive a plug that includes connecting contacts. A colloidal gel, of either polyurethane or silicone may be used in the housing to provide environmental protection for connectors, such as telephone jacks. Connectors wrapped with cured strips of sufficiently cohesive gel provide further protection. As an added feature, the colloidal gel contains particles that will absorb electromagnetic radiation.
U.S. Pat. No. 4,824,390 describes an electrical connector, especially for telecommunications, including an electrical insulating block having an array of cavities filled with an electrically insulating silicone gel surrounding electrical connections and contacts disposed in each of the cavities. The gel is deformable and penetrable at ambient temperatures to allow insertion of external electrical contacts into cavities to enable formation of electrical connections with the contacts in the cavities.
Recent developments of cured polymer compositions led to a preference for silicone materials that provide gel structures for filling or covering connectors of the types described previously. Connector cavities may first be filled with curable compositions that cure to gels when heated at elevated temperature. Information relating to thermally cured silicone compositions may be found in a number of references including U.S. Pat. No. 4,337,332 disclosing a latently curable organosilicone composition stabilized against premature gelation by the presence of an amount of an unsaturated amide that is sufficient to inhibit gelation of the composition at low, ambient or room temperature but insufficient to prevent hydrosilation at an elevated temperature. U.S. Pat. No. 4,511,620 describes an organosiloxane gel that cures by a hydrosilation reaction when heated.
Thermal curing involving a hydrosilation mechanism is known for providing silicone coatings and adhesives as described in U.S. Pat. No. 5,741,552, U.S. Pat. No. 5,466,532 and U.S. Pat. No. 6,004,679. Such materials typically comprise a vinyl-terminated polydiorganosiloxane; a hydrogen-substituted polydiorganosiloxane; and a hydrosilation catalyst. U.S. Pat. No. 5,059,484 describes gum-type organosiloxane elastomers having increased adhesion to organic polymer substrates following thermal curing using a platinum-catalyzed hydrosilation reaction in the presence of an amount of silanol-functional polydiorganosiloxane.
A disadvantage of thermally cured gels is the need for curable compositions to withstand elevated temperatures during conversion to cured polymer. Also, key reactants typically require separation into two parts to be mixed together just prior to curing. A reaction inhibitor may be required to prevent premature crosslinking after mixing in the presence of a thermally activated hydrosilation catalyst. Some of these problems may be avoided using curable compositions including a photoreactive hydrosilation catalyst rather than its thermally activated counterpart.
Previous studies described in U.S. Pat. No. 4,510,094, U.S. Pat. No. 4,530,879, U.S. Pat. No. 4,600,484, U.S. Pat. No. 4,916,169, U.S. Pat. No. 5,145,886, U.S. Pat. No. 6,046,250, EP 398,701, EP 561,893 and Mayer et al (J. Polymer Sci., Part A: Polymer Chem.; Vol. 34, No. 15, p. 3141-3146 (1996)) reveal the use of hydrosilation photocatalysts for curing silicone compositions containing vinyl and hydrosilyl functionality. There is nothing to suggest application of photocured silicone compositions as coatings or gels suitable for protecting connectors used in electrical networks.
Mayer et al (J. Polymer Sci., Part A: Polymer Chem.; Vol. 34, No. 15, p. 3141-3146 (1996)) presents findings from investigating trimethyl (β-dicarbonyl) Pt (IV) complexes as alternatively useful photocatalysts for the radiation-activated hydrosilation of silicone polymers. Typical silicone compositions were given as Si—H/Si-vinyl (SiH:Vi) molar ratio of 1.7 of two commercial silicones RP1 and RP2 with catalyst added to obtain 250-300 ppm elemental platinum in the mixture. Films were deposited with a controlled thickness of 20-25 μm on a KBr crystal window and exposed to the filtered HPK125W (UV) light from a medium pressure UV lamp. Disappearance of the Si—H frequency was followed using IR spectroscopy. The paper gives no information concerning protective sealing gels.
The previous discussion shows that gel sealants may be used for environmental protection of connector systems used in electrical and electronic networks. Room temperature curing and elevated temperature curing of silicone-based gel compositions are known, including those curing via a hydrosilation mechanism. Both thermal catalysts and photocatalysts have been described for promoting hydrosilation during curing of polysiloxane compositions. Regardless of information available concerning preparation and curing of polysiloxane compositions for a variety of applications, a need still exists for improved adhesion of cured polymers to organic resins that may be selected as molding materials for wire conductors and optical fiber connecting plugs and sockets used in network interface devices. Sealing gels with improved adhesion extend the lifetime of interconnect devices because they are less susceptible to displacement from connector sockets by repeated insertion and removal of plug elements.